Blackberry rooting for double crop production

Considering the increased consumer interest in fresh blackberries (Rubus spp.), fruit must be available in supermarket shelves all year round. This encourages off-season production in Portugal, mainly from September to December. Growers use long canes in order to harvest fruit during this period. Considering the extension of the vegetative growth cycle in mild winter climates, cane management is difficult due to excessive vegetative vigor. A trial was setup in order to evaluate the possibility of utilizing this excessive vigor for a double cropping system in blackberry. In non heated greenhouses, nine blackberry cultivars of different types were evaluated for their suitability for double cropping in early spring (soil) and late autumn (substrate). For each cultivar, two floricane suppression treatments (cutting and no cutting) were applied at the beginning of spring 2011. Four rooting treatments, including tip layering, tip layering followed by cold storage for 15 days after detachment from the stock plant, tip layering using 20-cm tipped primocanes, and simple layering, were also tested during summer 2011. Plants grown without floricanes produced longer primocanes and more nodes per primocane but had smaller cane diameters. Long canes were obtained from each cultivar, except 'Logan Thornless'. In December, one cultivar for each blackberry type was cold-stored from January to June 2012 and then cropped in non-heated tunnels, where they produced fruit from late August to late October. Yields ranged from 0.8 to 4.6 kg plant(-1) in the spring (all cultivars) and from 0.9 to 2.3 kg plant(-1) in autumn ('Chester Thornless' and 'Olallie' only). The results indicated that double cropping may be economically possible in blackberry using certain cultivars.